Multitube self-pulsing oscillator



Nov. 18, 1947. c, D, E TNER 2,431,179

I MULTI-TUBE SELF-PULSING OSCILLATOR Filed Oct. 3, i942 I INVENTOR. CARROLL 0. filvm/m.

ATTORNEY Patented Nov. 18, 1947 MULTITUBE SELF-PULSING OSCILLATOR Carroll D. Kentner, Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application October 3, 1942, Serial No. 460,670

18 Claims.

This invention relates to pulse type transmitters, and particularly to apparatus for producing pulses of high frequency energy, preferably of very short duration, with relation to the time intervals between pulses.

An object of the present invention is to provide a simplified and improved multi-tube high frequency pulse type transmitter which controls its own on and off periods (i. e., self-pulsing).

Another object is to provide a stabilized selfpulsing multi-tube high frequency pulse type transmitter wherein the anodes are at zero radio frequency potential and the system as a whole operates at only one frequency.

A further object is to provide a simplified high frequency pulse type transmitter having an even number of tubes arranged in a circle and wherein the grids constitute input electrodes and the filaments output electrodes, both of which are symmetrically arranged both from a physical and electrical standpoint.

A more complete description of the invention follows in conjunction with a drawing, wherein the single figure illustrates, by way of example only, one embodiment of the improvement multitube self-pulsing transmitter.

In the drawing, there are shown an even number of vacuum tubes 6 to 8, inclusive, each of which has anode, grid and filament electrodes. These vacuum tubes are shown arranged in a ring or circle symmetrically with respect to one another from both a physical and electrical standpoint. The anodes are all connected in parallel to a common ring-like conductor 9 to which is supplied a suitable positive polarizing potential from a source whose terminal is labeled B+. The grids of tubes I and 2 are connected together through a parallel conductor tuned circuit II] in push-pull relation, whereby the grids of these tubes have opposite instantaneous polarities. Similarly, the grids of tubes 3 and 4, 5 and 6, and l and 8 are connected together in push-pull relation through tuned circuits ll, l2 and [3, as shown. The tuned circuits W, H, H and I3 are individually adjustable by means of short circuiting bars it which are slidable over the lengths of their respective tuned circuits. All of the shorting bars I4 are connected at their centers to a common grid bias arrangement composed of a. resistor R and a condenser C in parallel. The filaments of vacuum tubes 2 and 3 are each supplied with suitable heating current through conductors surrounded by outer conductors l 5 and it which together constitute a tuned circuit for the filaments of the vacuum tubes 2 and 3. Tubular outer conductors l5 and it are strapped together and connected to ground at H. A short circuiting bar or slider l8, movable over the outer surface of the conductors l5 and it, serves to tune the filament circuit. The filaments of the tubes 2 and .i are thus arranged in push-pull relation for the radio frequency currents and in parallel relation for the low frequency heating current. These filaments receive opposite instantaneous polarities. The filaments of tubes 4 and 5 are similarly connected together in pushpull, and the tubes 5 and l, and 8 and I, also have their filaments respectively connected together in push-pull relation for the radio frequency currents. It will thus be seen that while the grids of two adjacent tubes in the ring or circle are connected together in push-pull by one tuned circuit, the filaments of these tubes are respectively connected in push-pull relation with the filament of a succeeding or preceding tube. The filaments of all tubes are supplied with heating current from a common heating source through a transformer is. Output energy is derived from the system through the various filament turn-edcircuits which are connected to a common output circuit. In the arrangement illustrated, each filament tuned circuit is connected through a pair of coductors 20 to a pair of bus connections 2!, 22. The instantaneously positive connections of the various leads 2B, 20 are connected to one bus (in this case 2!) while the instantaneously negative connections of the leads 2!), 2B are connected to another bus (in this case 22). The instantaneous polarities on the various electrodes at one particular instant in the operation of the circuit are illustrated by the plus and minus signs. A suitable output circuit (in this case a pair of leads 23) is connected to the two bus wires 2! and 22. The leads 23 will usually be connected to a transmission line extending to an antenna. It will thus be seen that all of the filament tank circuits contribute to the output energy taken from the system.

In effect, the anodes which are all connected together through a common bus 9 are grounded for the operating radio frequency energy. If desired, a radio frequency lay-pass condenser can be connected between bus 9 and ground.

A suitable source of alternating current (herein labeled sixty cycles) serves to change the net grid bias on the tubes and to trigger the tubes for operation at a particular point in the cycle. In effect, this sixty cycle current stabilizes or controls the pulse rate of the entire system. It should be noted that this alternating current source (here shown as sixty cycles) is connected in series with the grid resistor R through an adjustable tap on coil 2'5 and a transformer 24. In this way the pulse rate or repetition frequency of the pulses generated by the trans mitter of the invention is maintained at the frequency of the alternating current source supplied to the coil 25. It should be understood that the sixty cycle source shown is merely illustrative of any desired audio frequency pulse rate, which may be anywhere in the range from, let us say, thirty to three hundred cycles per second.

The operation of the system will now be given: Let us consider only one tube, since what follows applies equally to all tubes of the system. Assuming that the anode polarizing voltage is first connected to the anode, then the grid bias which is determined by the value of resistor R and the grid current drawn by the tube will be at about zero potential relative to the filament. This low value of bias will permit a surge of current to flow in the anode circuit. Such a surge will set up the conditions necessary for oscillations to begin, at a frequency determined by the tuning of the filament circuits l5, [6. etc., and the grid circuits I0, I I, etc. A portion of the total radio frequency voltage so developed will exist between the grid electrode and the filament electrode of each tube, and this voltage will be of sufficient amplitude to drive the grid positive with respect to the filament, thus causing grid current to flow. This flow of current through each tube will produce a negative charge on the condenser C and this negative charge will increase with time until the negative charge reaches a value equal to or slightly greater than the peak radio frequency grid voltage, at which time the vacuum tube will cease conducting. After a period of time determined by the value of the high resistor R, the negative charge on the condenser C will leak off through the resistor and thus permit oscillations to start and current again to flow through each tube. This cycle of operation will repeat itself. It will thus be seen that the operation of the system is essentially like a blocking oscillator, wherein each tube passes current momentarily and after a period of time blocks itself through the creation of a negative charge on the condenser in the grid circuit.

The values of the condenser C and the internal grid-filament resistance of the tube determines the length of the time for each pulse of current through the tube. The product of the values of resistor R and condenser C determines the pulse rate or repetition frequency. This pulse rate or repetition frequency is preferably stabilized by utilizing the audio frequency alternating current source (here labeled sixty cycles) which is impressed in series with the resistor R. The time constant of the RC circuit corresponds to a slightly lower frequency than the stabilizing audio frequency looking or pulsing voltage.

All the tubes will conduct simultaneously and will cease conducting simultaneously. The current flow through the tubes is made to be extremely short compared to the intervals between the pulses of current flow, and the length of current flow through the tubes is adjustable, depending upon the value of the condenser C and the internal impedance of the tubes. Inasmuch as it is not feasible to adjust the internal tube impedance in order to obtain an adjustment of the length of each pulse of current through the tube, the condenser C is made adjustable. Thus, it is positioned to obtain any desired ratio of on time to off time, which expressed in percentage is known as the duty cycle. The resistor R is also made adjustable in order to aid in adjusting the repetition frequency of the pulses.

In one embodiment of the invention tried out in practice, the pulse'time (that is, the length of seconds.

employed for stabilizing the pulse rate.

each pulse of current through the tubes of the system) was made to be variable from one to ten microseconds, while the time interval between pulses was made to be about 16,600 micro- A sixty cycle alternating current was v The radio frequency range of the system was adjustable between 190 to 200 megacycles. The tubes were arranged in a ring or circle symmetrical with respect to one another, both from physical and electrical standpoint. The filament leads extended straight down from the tubes in a vertical direction through their surrounding tubular conductors, whereas the grid leads extended in an opposite direction (that is, straight upwards) to their respective tuned circuits. Thus, the filament tank circuits were on opposite sides of the tubes relative to the grid tank circuits. Any even number of vacuum tubes were employed. It should be clearly understood that these figures are merely given as an illustration and that, if desired, it is a relatively simple matter to obtain a wider radio frequency range than that mentioned above and a different duty cycle.

The invention has several advantages, among which are (1) the grounding of the filament circuits enables the selection of an output circuit which has no direct current potential thereon, thus simplifying operational problems; (2) the arrangement of the invention enables a given tube to be operated at much higher frequencies than would be the case if tuned circuits were employed in the anode connections in accordance with conventional practice. This is because the system of the invention prevents the tube capacities from being additive across any one tank circuit which would be the case if the tubes were connected in push-pull parallel; (3) the transmitter of the invention provides tight couplin between the various tank circuits involved, which is an essential condition to enable the transmitter as a whole to oscillate at one and only one frequency; (4) the system provides a simplified control in which the grid circuit tuning primarily governs the frequency while the filament tuning controls the feed back or regeneration; and (5) the self-pulsing arrangement of the improved transmitter enables a simplification which decreases the size, weight, and cost of the system compared to known systems having external keying circuits.

Although the output circuit has been illustrated as directly connected to the filament tank circuits, it should be understood that the coupling between the output circuit and the filament tank circuits can be inductive, capacitive or conductive. Further, although eight tubes have been illustrated, it should be understood that any even number of tubes can be employed, ranging from.

two upwards, provided the principles of the invention are followed out.

What is claimed is:

1. A multi-tube self-pulsing generator of radio frequency pulses comprising a pair of vacuum tubes each having a filament, a grid, and an anode, a first tuned circuit connected between the grids of said tubes, a second tuned circuit connected between said filaments, whereby opposite instantaneous polarities appear on the grids of said tubes and opposite instantaneous polarities also appear on the filaments of said tubes, a low impedance connection between said anodes, whereby said anodes are at zero radio frequency potential, a resistor shunted by a condenser connected to said first tuned circuit, and an output circuit coupled to said second tuned circuit, the values of said resistor and condenser determining the pulse rate of said generator.

2. A multi-tube generator of radio frequency pulses comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle, and each having a filament, a grid and an anode, a tuned circuit connected in push-pull relation between the rids of each pair of tubes, a tuned circuit connected in push-pull relation between the filament of each tube of said pair and the filament of an adjacent tube of another pair, and connections of low impedance to energy of the operating frequency between the anodes of all said tubes.

3. A multi-tube generator of radio frequency pulses comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle, and each having a filament, a grid and an anode, a tuned circuit connected in push-pull relation between the grids of each pair of tubes, a tuned circuit connected in push-pull relation between the filament of each tube of said pair and the filament of an adjacent tube of another pair, connections of low impedance to energy of the operating frequency between the anodes of all said tubes, and a resistor and condenser combination connected in common to the grids of all of said tubes.

4. A multi-tube generator of radio frequency pulses comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle and each having a filament, a grid and an anode, a lecher wire tank circuit connected in push-pull relation between the grids of each pair of tubes, a tank circuit of uniformly distributed constants connected in push-pull between the filament of each tube of said pair and the filament of an adjacent tube of another pair, direct connections between the anodes of all of said tubes, and a common grid leak and grid condenser combination for the grids of all of said tubes.

5. A multi-tube generator of radio frequency pulse comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle and each having a filament, a grid and an anode, a tuned circuit of uniformly distributed constants connected in push-pull relation between the grids of each pair of tubes, a tuned circuit of uniformly distributed constants connected between the filament of each tube of said pair and the filament of an adjacent tube of another pair, short circuiting bars for each tuned circuit, direct connections between the anodes of all of said tubes, and a common grid leak and shunt grid condenser combination for the grids of all said tubes.

6. A multi-tube generator of radio frequency pulses comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle and each having a filament, a grid and an anode, a tuned circuit of uniformly distributed constants connected in push-pull relation between the grids of each pair of tubes, a tuned circuit of uniformly distributed constants connected between the filament of each tube of said pair and the filament of an adjacent tube of another pair, a short-circuiting bar for each tuned circuit, direct connections between the anodes of all of said tubes, a common grid leak and shunt grid condenser combination for the grids of all said tubes, and means for applying audio frequency voltage in series with said resistor for stabilizing the pulse rate of said generator.

'7. A multi-tube self-pulsing generator of radio frequency pulses comprising a pair of vacuum tubes each having a filament, a grid, and an anode, a first tuned circuit connected between the grids of said tubes, a second tuned circuit connected between said filaments, whereby opposite instantaneous polarities appear on the grids of said tubes and opposite instantaneous polarities also appear on the filaments of said tubes, a low impedance connection between said anodes, whereby said anodes are at zero radio frequency potential, a resistor shunted by a condenser connected to said first tuned circuit, an output circuit coupled to said second tuned circuit, the values of said resistor and condenser determining the pulse rate of said generator, and a source of audio frequency alternating current for applying an alternating voltage in series with said resistor for stabilizing the pulse rate of said generator.

8. A generator of periodic high frequency pulses of the order of 200 megacycles and of very short diuation compared to the time intervals between pulses, comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle and each having a filament, a grid and an anode, a tuned circuit of uniformly distributed constants connected in push-pull relation between the grids of each pair of tubes, a tuned circuit of uniformly distributed constants connected between the filament of each tube of said pair and the filament of an adjacent tube of another pair, a short-circuiting bar for each tuned circuit, direct connections between the anodes of all of said tubes, and a common grid leak and shunt grid condenser combination for the grids of all of said tubes, the product of the values of said resistor and condenser determining the pulse rate of said generator.

9. A generator in accordance with claim 8, including a source of low frequency voltage in series with said resistor for stabilizing th pulse rate of said generator.

10. A generator of periodic high frequency pulses of the order of 200 megacycles and of very short duration compared to the time intervals between pulses, comprising a pair of vacu um tubes each having a filament, a grid, and an anode, a first tuned circuit connected between the grids of said tubes, a second tuned circuit connected between said filaments, whereby opposite instantaneous polarities appear on the grids of said tubes and opposite instantaneous polarities also appear on the filaments of said tubes, a low impedance connection between said anodes, whereby said anodes are at Zero radio frequency potential, a resistor shunted by a condenser connected to said first tuned circuit, an output circuit coupled to said second tuned circuit, the values of said resistor and condenser determining th pulse rate of said generator, and means for changing the values of said resistor and condenser.

11. A multi-tube generator of radio frequency pulses comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle and each having a filament, a grid and an anode, a tuned circuit connected in push-pull relation between the grids of each pair of tubes, 21. tuned circuit connected in push-pull relation between the filament of each tube of said pair and the filament of an adjacent tube of another pair, connections of low impedance to energy of the operating frequency between the anodes of all said tubes, a resistor shunted by a condenser connected in common to the grids of all of said tubes, and a source of audio frequency alternating current applying an alternating voltage in series with said resistor for stabilizing the pulse rate of said generator, the time constant of said resistor-condenser combination corresponding to a lower frequency than the audio frequency of said source.

12. A multi-tube generator of radio frequency pulses comprising a plurality of pairs of vacuum tubes arranged symmetrically in a circle, and each having a filament, a grid and an anode, a tuned circuit connected in push-pull relation between the grids of each pair of tubes, a tuned circuit connected in push-pull relation between the filament of each tube of said pair and the filament of an adjacent tube of another pair, connections of low impedance to energy of the operating frequency between the anodes of all said tubes, a resistor shunted by a condenser connected in common to the grids of all of said tubes, and a source of audio frequency alternating current in the range between thirty cycles and three hundred cycles applying an alternating voltage in series with said resistor for stabilizing the pulse rate of said generator, the time constant of said resistor-condenser combination corresponding to a lower frequency than the audio frequency of said source.

13. A multi-tube generator of radio frequency pulses comprising a pair of vacuum tubes each having a filament, a grid and an anode, a tuned circuit connected between the grids of said tubes, whereby opposite instantaneous polarities appear on said grids, a resistor shunted by a condenser connected to said tuned circuit, connections to said filaments for producing opposite instantaneous polarities on said filaments, a low impedance connection between said anodes, whereby said anodes are at a, fixed radio frequency potential, and an output circuit coupled to said filament connections, the values of said resistor and condenser determining the pulse rate of said generator.

14. A multi-tube generator of radio frequency pulses comprising a pair of vacuum tubes each having a filament, a grid and an anode, a tuned circuit connected between the filaments of said tubes, whereby opposite instantaneous polarities appear on said filaments, connections to the grids of said tubes for producing opposite instantaneous polarities on said grids, a resistor shunted by a condenser connected to said grid connections, a low impedance connection between said anodes,

whereby said anodes are at a fixed radio frequency potential, and an output circuit coupled to said filament tuned circuit, the values of said resistor and condenser determining the pulse rate of said generator.

15. A multi-tube generator comprising a plurality of pairs of vacuum tubes arranged in a circle, each of said tubes having a filament, a grid and an anode, tuned circuitsbetween the grids of said pairs of tubes for producing opposite instantaneous polarities on the grids of each pair of tubes, tuned circuits between the filaments of the tubes in different pairs for producing opposite instantaneous polarities on said filaments, connections of low impedance to energy of the operating frequency between the anodes of all of said tubes, and an output circuit coupled to said filament tuned circuits.

16. A generator of pulses of high frequency energy comprising a high frequency blocking oscillator having a condenser and a resistor controlling the pulse rate, said oscillator producing 17. A generator of pulses of high frequency energy comprising a high frequency multi-electrode electron discharge device oscillator, said oscillator producing radio frequency oscillations whose frequency is measured in megacycles, said oscillator including an anode which is at zero radio frequency potential for energy of the operating frequency, a condenser in circuit with an electrode of said oscillator, said condenser having such value that in combination with the internal resistance of said device it determines the time duration of each pulse of radio frequency energy produced by said oscillator, a resistor in shunt to said condenser, the product of the values of said resistor and condenser determining the pulse rate, and a source of low frequency energy coupled to said resistor and condenser for stabilizing the pulse rate, and means for deriving spaced bursts of radio frequency potential from said oscillator.

18. A generator of radio frequency pulses comprising a, radio frequency vacuum tube oscillator having a grid, an anode, and a filament, a condenser in circuit with said grid, said generator producing radio frequency oscillations whose frequency is measured in megacycles, said generator being so constructed and arranged that said anode is at zero radio frequency potential for energy of the operating frequency, said condenser having such value that in combination with the internal grid-filament resistance of said tube it determines the time duration of each pulse ofradio frequency energy produced by said oscillator, a resistor in shunt to said condenser, the product of the values of said resistor and condenser determining the pulse rate, and a source of sine waves of audio frequency coupled to said resistor and condenser for stabilizing the pulse rate, the time constant of said resistor and condenser corresponding to a frequency slightly lower than the frequency of said audio source, and means coupled between the anode and the filament circuit for deriving spaced bursts of radio frequency energy from said oscillator.

CARROLL D. KENTNER.

REFERENCES CITED The following references are of record. in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,007,662 Prinz July 9, 1935 2,081,425 Fay May 25, 1937 1,649,753 Strauss Nov. 15, 1927 1,698,290 Alexanderson Jan. 8, 1929 1,776,381 Chireix Sept. 23, 1930 1,621,034 Slepian Mar. 15, 1927 2,297,742 Campbell Oct. 6, 1942 2,358,297 Bedford Sept. 19, 1944 1,950,400 Curtis Mar. 13, 1934 1,896,417 Page Feb. 7, 1933 2,189,402 Pasma Feb. 6, 1940 2,382,954 Beaudoin Aug. 21, 1945 Disclaimer 2,431,179.-Oarroll D. Kenmer, Merchantville, N. J. MULTITUBE SELF-PULSING OSCILLATOR. Pateht dated Nov; 18, 1947. Disclaimer filed May 26, 1950, by the assignee, Radio Corporation of America. Hereby entrs this disclaimer to claims 2 and 15 of said patent. I

[Oflicial Gazette June 20, 1950.] 

